1. Field of the Invention
The present invention generally relates to a well pumping unit and, more particularly, a hydraulically operated oil well pumping unit utilizing hydraulically powered piston and cylinder assemblies oriented vertically for reciprocating a slide assembly having flexible members entrained over rotatable wheels or pulleys mounted thereon with one end of the flexible members being anchored and the other end connected to the polish rod of the oil well pump assembly so that the polish rod and operating piston of the pump unit will move a linear distance twice the linear movement of the slide assembly with the hydraulic system operating the cylinders including an accumulator for storing energy produced by gravity induced downward movement of the pump rod and other reciprocating pump components by movement of hydraulic fluid from the lower ends of the cylinders into the accumulators with this stored energy being automatically used to assist in upward lift of the pump components when the polish rod and other components are being lifted thereby increasing the efficiency of the pumping unit.
2. Description of the Prior Art
Conventional oil well pumping units utilize pump jacks which include an elongated oscillating beam having a horsehead at one end connected with a cable system attached to the upper end of the polish rod and a massive, counterweighted drive system connected to the opposite end of the beam. Such devices are quite costly due to their extremely heavy weight and various structural components. When it is necessary to adjust the stroke or vary the frequency of the cycles of operation, it is necessary to completely shutdown the pumping unit for several hours, usually four to six hours. Additionally, the shipping cost is high due to the weight of such units and when maintenance is required, such as rebuilding the unit, the components are costly and considerable shutdown time is required. Efforts have been made to utilize fluid pressure operating units in which piston and cylinder assemblies have been connected to the oscillating beam as a replacement for the massive mechanical drive system, but as a general rule, such devices have not replaced the conventional pump jack. The following U.S. patents are exemplary of the prior art in this field of endeavor.
______________________________________ U.S. Pat. Nos.: 3,782,117 U.S. Pat. Nos.: 1,758,453 4,191,010 1,888,621 3,072,219 2,310,001 Re.25,432 2,169,815 3,977,680 2,432,735 1,379,378 2,915,919 4,037,662 3,264,942 3,739,853 4,099,447 2,949,960 4,201,115. ______________________________________